The present invention relates to a quick release chuck for surgical and dental instruments, particularly for high speed instruments powered by rotary air motors. The chuck engages the shafts of drills or burs and is actuated without the use of additional tools. Another advantage of the present invention is realized through incorporation of a self-locking feature which requires a minimum amount of torque to activate and provides insurance against inadvertent loosening of the locking mechanism.
Small hand-held high-speed drills having substantial torque are necessary in the performance of bone surgery. Although small and light weight so as to minimize surgeon fatique during lengthy surgical procedures, the devices are designed and manufactured with utmost precision for minimum unbalance and vibration at high rotational speeds. While the drills used by surgeons and dentists are somewhat similar in size and purpose and use many of the same drills and burs, the instruments are generally different. Dental drills are usually smaller in size, have a higher rotational speed and require less torque and, hence, usually use an air turbine for power. While surgical drills also use air turbines, many, including those for which the present device is intended, use an air motor, which provides greater torque and slightly lower velocity. The greater torque, in turn, places more stringent requirements for drill and bur engagement which are not met by the many surgical drill chucks which have evolved from dental drill designs.
During the course of a surgical operation, it is necessary for the surgeon to frequently remove and replace the drill or bur with a different sized tool or merely to replace one that has become dulled. Minimization of time is important and frequently critical during a surgical procedure. Frequent replacement of dulled burs with new sharp burs can speed bone cutting but, in terms of overall time, only if the burs can be replaced quickly. The use of wrenches, keys or other tools to implement bur replacement is undesirable because such use of tools not only delays the replacement but frequently such tools can be misplaced causing even longer intolerable delays. Almost all modern surgical drills accommodate quick release chucks which can be actuated without the use of auxiliary tools. The fact that these quick release chucks are available in countless different designs would appear to confirm that design deficiencies still exist.
Early dental drills used a simple chuck mechanism which was merely a resilient plastic or rubber sleeve. When the sleeve wore to the point where excessive slippage occurred, it was replaced. Obviously, such devices would be impractical for surgical usage because of the need for greater torque and greater precision in surgical procedure. Slippage would be intolerable. For similar reasons, the resilient slotted metal chuck of Thorburn U.S. Pat. No. 3,869,796 would be acceptable for dental purposes but not for surgical usage.
Lieb U.S. Pat. No. 3,893,242 describes a compact air-turbine powered dental hand piece which requires the use of a novel auxiliary wrench for changes of burs. As previously mentioned, the use of such wrenches is extremely inconvenient for surgical use.
Hagen U.S. Pat. No. 3,835,858 and Nordin U.S. Pat. No. 3,867,943, both describe surgical drills which require interchange of the entire hand piece containing not only the cutting bur but also support bearings, clutch, housing, etc. While the use of a bur guard and support is obviously necessary with certain long shafted burs, replacement of such complex components each and every time that the burs become dulled is excessively expensive. In addition, while these devices have the advantage that the burs can be changed while the motor is rotating, they have the disadvantage that it is difficult to replace the hand piece when the motor is not rotating. Further, the snap action closure is a potential source of trouble since the hand piece can be easily and inadvertently dislodged during usage.
Shea U.S. Pat. No. 4,007,528 describes another common means of bur shank engagement with a plurality of spherical detents which engage a circumferential groove on the shank. While the balls provide good retention for the shank, they provide poor torque transmission so they are usually found in conjunction with a flat end or other non-circular shank ending which mates with a complementarily shaped driving surface on the shaft. This not only increases the cost of the drills and burs but can also cause delay and confusion during the course of an operation since each different drill requires its own set of cutting tools which are not interchangeable with instruments of other designs.
Ideally, the surgical drill chuck should allow the use of simple low cost drills and burs having straight, non-complex shafts which could be used interchangeably with various power drill designs and which could be economically replaced and/or discarded as they become dulled.
Hedrick U.S. Pat. No. 3,674,281 describes a drill chuck which meets many of these objectives. A plurality of ball elements are frictionally pressed against the drill or bur stem by a wedge shaped sleeve under pressure of a compression spring. The sleeve can be retracted by action of an external manually actuated lever to allow the balls to retract from the drill shaft so that the drill can be removed and replaced. The chuck allows for use of low cost drills and burs having simple shaft designs.
A problem inherent in the design of the Hedrick chuck is the use of spherical balls to establish driving contact with the drill stem. With the use of modern high-torque air motors which provide fast cutting action in dense bone, the point to point contact between chuck and drill stem is inadequate and slippage results in lack of rotation and damage to the drill stem. Also the manually operated release lever is inconveniently located and frequently results in inadvertent release of the bur during crucial times, a problem common to many prior art surgical drill chucks.
Other prior art structures are shown in Hanson U.S. Pat. Nos. 1,582,010; Witt 2,010,210; Sindelar 3,428,327; Herman 3,684,302; Wanner 3,929,343; Bent 3,975,032 and Norlander French Patent No. 961,920.